The present invention relates to a semiconductor device and a manufacturing method thereof, and particularly can be used appropriately for a semiconductor device including a static random access memory and a manufacturing method of such a semiconductor device.
An SRAM (Static Random Access Memory) is a type of semiconductor memory. One SRAM memory cell includes two access transistors, two drive transistors, and two load transistors so that the six transistors need to be formed over a semiconductor substrate. Accordingly, there is a limit to a reduction in the area occupied by the SRAM memory cell.
To eliminate the limit, a so-called advanced SRAM has been proposed in which, to the two load transistors among the six transistors, thin-film transistors (TFTs) are applied. In the advanced SRAM, by forming the load transistors made of the thin-film transistors over the interlayer insulating film covering the access transistors and the drive transistors, the stacked configuration of the SRAM memory cell has been implemented.
In the advanced SRAM, the source regions of the access transistors and the drain regions of the drive transistors are coupled to local lines in an upper layer via polysilicon plugs (bit-line storage contact plugs) formed between the gate electrodes of the access transistors and the gate electrodes of the drive transistors and polysilicon plugs (storage node contact plugs) formed between bit lines and ground lines. The source regions and the drain regions thereof are further electrically coupled to the load transistors or the like via the local lines. Note that examples of Patent Document disclosing such an advanced SRAM include Patent Document 1.